Crown-Rump Length Calculator
Estimate gestational age and estimated due date from a first-trimester ultrasound Crown-Rump Length (CRL) measurement.
What Crown-Rump Length measures
Crown-Rump Length (CRL) is the length of an embryo or fetus from the top of the head to the bottom of the buttocks, measured by ultrasound. It is the most accurate way to date a pregnancy during the first trimester, typically between about 6 and 13 weeks.
The formula used
This calculator uses the widely-used Robinson formula: Gestational Age (days) = 8.052 x sqrt(CRL in mm) + 23.73. This estimate is most accurate for CRL measurements roughly between 15 and 95 mm, corresponding to the late first trimester.
This tool is for general educational purposes only and does not replace a formal ultrasound report or dating scan interpreted by a qualified sonographer or physician. Always rely on your healthcare provider’s official pregnancy dating.